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Healthy planet, tired people?

No need to squint: Cities are changing their street lighting systems to help cut down on energy use. The U.S. Department of Energy estimates that replacing 300 traditional streetlights with LED fixtures would save about $15,000 a year on energy and maintenance cost. Officials also say the switch would reduce annual carbon dioxide emissions by 75 tons.

But some health organizations are cautioning against the light-emitting diode fixtures. That’s because the light produced by LEDs is in the blue spectrum of light — that is, their wavelengths are shorter. This kind of light blocks the body’s production of melatonin, the hormone that lulls us to sleep at night, and activates neurons associated with alertness. While blue light is good for us during the day, it’s bad for us at night, something noted by health researchers looking at blue light emitted by cell phones and other devices.

The American Medical Association also points to blue light’s effect on melatonin production, and estimates LED lamps have a fivefold greater impact on circadian sleep rhythms than traditional street lamps. In surveys, people report that they sleep less, and sleep less well, in residential areas with brighter nighttime lighting. When our circadian rhythm gets off, it could contribute to cancer, heart disease and diabetes, according to Harvard Health Publications.

The AMA is encouraging cities that install street and other outdoor lighting use the lowest emission of blue light possible, and for all lighting to be shielded to minimize glare and light pollution. While the main goal may be to cut down carbon dioxide emissions, we should do so in as healthy a way as possible.